wachtelhund1
Member
I have a H&R model 700 .22 Mag, semi-auto which I’m considering converting to 5.7X28 mm or a version of it. I re-barreled this gun two years ago with a Green Mountain 22" fluted barrel and thought about converting it then, but decided not to based on the cost of ammo. Now once fired brass is available. I’m also concerned at what the long term .22 Mag ammo cost will be after this .22 LR shortage is over. Having a reloadable cartridge with slightly better .22 Mag ballistics would be nice. I shoot a lot in my back yard.
I wouldn’t consider this with any other .22 Mag semi-auto rifle, as they are all blow back actions. The 5.7x28 is a 50,000 PSI round vs. 25,000 PSI for the .22 Mag.
So why the H&R 700 .22 Mag?
The barrel is threaded into the receiver, 18 tpi; not pinned.
The new barrel is a Green Mountain 22”, 1:14 twist vs. the common 1:16 twist of rimfire barrels.
The H&R 700 has a double rail recoil system with recoil spring attached to the bolt to control the cycling, attached with two 5/8” nuts to the receiver.
An additional recoil spring can be slipped over the top of the original spring for the additional pressure of the 5.7X28 round. See picture.
The bolt is fairly simple and can be reproduced with the firing pin in the center.
This gun has 5 and 10 round magazines.
I don’t think there will be an issue with feeding, as I have worked the magazine to feed the 5.7 round, the bullet will enter the chamber before the case head clears the magazine lips.
Issues: 5.7x28 case is .082” longer than .22 mag, plus most .224 bullets are longer than those found in loaded .22 mag ammo.
COL for the 5.7x28 is 1.594" vs .22 mag @ 1.350”. So loading would be limited to 30, 35, 40 grain bullets.
The 5.7X28 shoulder needs to be set back about .070” to work in the magazine for this rifle. A collar could be used to short chamber the barrel and also make a sizing die.
This would help with COL and bullet seating. Case neck would be .182” plus .070” = .252, if left untrimmed. Loading a Speer .22 Hornet 33 Grain JHP, .438 length into the entire neck would leave .186 exposed for a COL of 1.323” just under the .22 mag COL. This bullet has the same shape as a .22 mag bullet.
Biggest Issue: Cycling. The 5.7X28 is a 50,000 psi pistol round. The .22 Mag is 25,000 psi. Barrel is CM .900" at the breech, receiver is 1.062 at the breech. PSI can be reduced some using slower rifle powder for the 22" barrel. Plus cycling can be controlled by adding additional recoil spring over the top of the existing one. Shoulder length increase will be an issue upon firing. Bottle neck case being fired in blow back action will lenghten.
Pros: Reloadable small round with slightly better .22 Mag ballistics,
.13 to 16 cents per round vs .20 to .25 cents for .22 Mag
Once fired brass now available.
Cons: Cost of conversion
Cost of dies
Thoughts Please!
I wouldn’t consider this with any other .22 Mag semi-auto rifle, as they are all blow back actions. The 5.7x28 is a 50,000 PSI round vs. 25,000 PSI for the .22 Mag.
So why the H&R 700 .22 Mag?
The barrel is threaded into the receiver, 18 tpi; not pinned.
The new barrel is a Green Mountain 22”, 1:14 twist vs. the common 1:16 twist of rimfire barrels.
The H&R 700 has a double rail recoil system with recoil spring attached to the bolt to control the cycling, attached with two 5/8” nuts to the receiver.
An additional recoil spring can be slipped over the top of the original spring for the additional pressure of the 5.7X28 round. See picture.
The bolt is fairly simple and can be reproduced with the firing pin in the center.
This gun has 5 and 10 round magazines.
I don’t think there will be an issue with feeding, as I have worked the magazine to feed the 5.7 round, the bullet will enter the chamber before the case head clears the magazine lips.
Issues: 5.7x28 case is .082” longer than .22 mag, plus most .224 bullets are longer than those found in loaded .22 mag ammo.
COL for the 5.7x28 is 1.594" vs .22 mag @ 1.350”. So loading would be limited to 30, 35, 40 grain bullets.
The 5.7X28 shoulder needs to be set back about .070” to work in the magazine for this rifle. A collar could be used to short chamber the barrel and also make a sizing die.
This would help with COL and bullet seating. Case neck would be .182” plus .070” = .252, if left untrimmed. Loading a Speer .22 Hornet 33 Grain JHP, .438 length into the entire neck would leave .186 exposed for a COL of 1.323” just under the .22 mag COL. This bullet has the same shape as a .22 mag bullet.
Biggest Issue: Cycling. The 5.7X28 is a 50,000 psi pistol round. The .22 Mag is 25,000 psi. Barrel is CM .900" at the breech, receiver is 1.062 at the breech. PSI can be reduced some using slower rifle powder for the 22" barrel. Plus cycling can be controlled by adding additional recoil spring over the top of the existing one. Shoulder length increase will be an issue upon firing. Bottle neck case being fired in blow back action will lenghten.
Pros: Reloadable small round with slightly better .22 Mag ballistics,
.13 to 16 cents per round vs .20 to .25 cents for .22 Mag
Once fired brass now available.
Cons: Cost of conversion
Cost of dies
Thoughts Please!
